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# PCJACOBI
Jacobi (i.e. diagonal scaling preconditioning) 
## Options Database Keys

- ***-pc_jacobi_type <diagonal,rowmax,rowsum> -*** approach for forming the preconditioner
- ***-pc_jacobi_abs -*** use the absolute value of the diagonal entry
- ***-pc_jacobi_fixdiag -*** fix for zero diagonal terms by placing 1.0 in those locations





## Notes
By using `KSPSetPCSide`(ksp,`PC_SYMMETRIC`) or -ksp_pc_side symmetric
can scale each side of the matrix by the square root of the diagonal entries.

Zero entries along the diagonal are replaced with the value 1.0

See `PCPBJACOBI` for fixed-size point block, `PCVPBJACOBI` for variable-sized point block, and `PCBJACOBI` for large size blocks


## See Also
  `PCCreate()`, `PCSetType()`, `PCType`, `PC`,
`PCJacobiSetType()`, `PCJacobiSetUseAbs()`, `PCJacobiGetUseAbs()`, `PCASM`,
`PCJacobiSetFixDiagonal()`, `PCJacobiGetFixDiagonal()`
`PCJacobiSetType()`, `PCJacobiSetUseAbs()`, `PCJacobiGetUseAbs()`, `PCPBJACOBI`, `PCBJACOBI`, `PCVPBJACOBI`

## Level
beginner

## Location
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/pc/impls/jacobi/jacobi.c.html#PCJACOBI">src/ksp/pc/impls/jacobi/jacobi.c</A>

## Examples
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/stag/tutorials/ex1.c.html">src/dm/impls/stag/tutorials/ex1.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/dm/impls/stag/tutorials/ex4.c.html">src/dm/impls/stag/tutorials/ex4.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex1.c.html">src/ksp/ksp/tutorials/ex1.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex15.c.html">src/ksp/ksp/tutorials/ex15.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex15f.F90.html">src/ksp/ksp/tutorials/ex15f.F90</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex1f.F90.html">src/ksp/ksp/tutorials/ex1f.F90</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex23.c.html">src/ksp/ksp/tutorials/ex23.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex2f.F90.html">src/ksp/ksp/tutorials/ex2f.F90</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex6.c.html">src/ksp/ksp/tutorials/ex6.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex7.c.html">src/ksp/ksp/tutorials/ex7.c</A><BR>
<A HREF="PETSC_DOC_OUT_ROOT_PLACEHOLDER/src/ksp/ksp/tutorials/ex71.c.html">src/ksp/ksp/tutorials/ex71.c</A><BR>


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[Edit on GitLab](https://gitlab.com/petsc/petsc/-/edit/release/src/ksp/pc/impls/jacobi/jacobi.c)


[Index of all PC routines](index.md)  
[Table of Contents for all manual pages](/manualpages/index.md)  
[Index of all manual pages](/manualpages/singleindex.md)